使用测试覆盖工具来检测代码库，然后运行应用程序本身，而不是测试。

Emma和Eclemma将为您提供关于在任何给定的代码运行中运行的类的百分比的良好报告。

我很惊讶这里竟然没有提到ProGuard。这是目前最成熟的产品之一。

ProGuard is a free Java class file shrinker, optimizer, obfuscator, and preverifier. It detects and removes unused classes, fields, methods, and attributes. It optimizes bytecode and removes unused instructions. It renames the remaining classes, fields, and methods using short meaningless names. Finally, it preverifies the processed code for Java 6 or for Java Micro Edition. Some uses of ProGuard are: Creating more compact code, for smaller code archives, faster transfer across networks, faster loading, and smaller memory footprints. Making programs and libraries harder to reverse-engineer. Listing dead code, so it can be removed from the source code. Retargeting and preverifying existing class files for Java 6 or higher, to take full advantage of their faster class loading.

下面是列表死代码的示例:https://www.guardsquare.com/en/products/proguard/manual/examples#deadcode

我会让运行中的系统保持代码使用的日志，然后开始检查几个月或几年没有使用的代码。

例如，如果您对未使用的类感兴趣，那么所有的类都可以在创建实例时记录日志。然后，一个小脚本可以将这些日志与完整的类列表进行比较，以找到未使用的类。

Of course, if you go at the method level you should keep performance in mind. For example, the methods could only log their first use. I dont know how this is best done in Java. We have done this in Smalltalk, which is a dynamic language and thus allows for code modification at runtime. We instrument all methods with a logging call and uninstall the logging code after a method has been logged for the first time, thus after some time no more performance penalties occur. Maybe a similar thing can be done in Java with static boolean flags...

Eclipse Goto Windows >首选项> Java >编译器>错误/警告 把它们都改成错误。修复所有错误。这是最简单的方法。这样做的好处是，您可以在编写代码时清理代码。

截图Eclipse代码:

一个工作得相当不错的Eclipse插件是未使用代码检测器。

它处理整个项目或特定文件，并显示各种未使用/死亡的代码方法，以及建议可见性更改(即可以保护或私有的公共方法)。

CodePro最近由谷歌和Eclipse项目一起发布。它是免费的，而且非常有效。该插件具有一个/多个入口点的“查找死代码”功能。效果很好。